1. Field of the Invention
The present invention relates to a dielectric filter installed on a communication apparatus, such as a portable telephone and a wireless telephone.
2. Description of the Prior Art
A conventional dielectric filter will be explained hereinafter.
FIG. 27 is a perspective view showing a conventional dielectric filter. Reference numerals 1 and 2 represent dielectric resonators comprising: dielectric base bodies 1a, 2a made of dielectric material, with centrally axially extending through holes 1b, 2b; outer conductors 1c, 2c surrounding outer surfaces of the dielectric base bodies 1a, 2a; inner conductors 1d, 2d provided along inner surfaces of the through holes 1b, 2b; and connecting conductors 1e and 2e connecting the outer conductors 1c, 2c and the inner conductors 1d, 2d. A reference numeral 5 represents a coupling substrate 5 comprising conductors 5a, 5b, 5c and 5d formed on a dielectric substrate (aluminum substrate or the like). This connecting substrate 5 realizes input/output coupling capacitances (one is between conductors 5a and 5c, the other between conductors 5b and 5d) and an interstage coupling capacitance (between 5a and 5b). FIG. 28(A) is a detailed front view showing the coupling substrate 5 of the conventional dielectric filter, and FIG. 28(B) is a detailed rear view showing the coupling substrate 5 of the conventional dielectric filter. Reference numerals 6 and 7 represent central conductors connecting the inner conductors 1d, 2d and the coupling substrate 5 electrically and mechanically. Reference numerals 8 and 9 represent input and output terminals which are connected to the conductors 5c, 5d of the coupling substrate 5 electrically and mechanically by means of solder or the like.
However, this kind of conventional dielectric filter inherently requires numerous components, such as the coupling substrate 5, central conductors 6, 7, and input/output terminals 8, 9. This encounters with the difficulty in reducing the size of a dielectric filter. Furthermore, mass-productivity is not good due to a large number of parts and time-consuming production process.